432 HANDBOOK OF ELECTRICAL ENGINEERING
Table 15.8. Protection alarms and indications for a high-voltage variable speed drive
Function Protection Alarm Indication- Open circuit, short circuit and
earth faults in the rectifier
including the faults in the
rectifier including the DC
link
X- Open circuit, short circuit and
earth faults in the inverter
including the cable and
motor
X- Overcurrent due to
commutation failure in the
rectifier
X- Overcurrent due to
commutation failure in the
inverter
X- Undervoltage at the output of
the inverter
X- Overfrequency at the output of
the inverter
X- Undervoltage at the input of
the rectifier
X- Enclosure over-temperatures X
- Control system faults X X
- Harmonic filter faults X X
- Single-phase operation of the
motor
XX- Overcurrent of the motor X X X
- Winding temperature of the
motor
XXX- Winding temperature of power
transformers
XXX- Supply line voltages X
- Supply line currents X
- DC link voltage X
- DC link current X
- Motor line voltages X
- Motor line current X
- Set-point frequency of inverter X
- Actual frequency of inverter X
- Motor speed X
local transformers may be sufficient to cause sensitivity in the performance of the filter with variations
in system loading. This is less of a problem where the plant is supplied from an overhead transmission
line, and the upstream MVA capacity is large compared with the total demand of the plant.
Drilling rigs and low capacity AC variable speed drives are usually six-phase systems. If these
are known to be needed at the conceptual stage of a project then their effects on other equipment